Motors may be classified into a direct current (DC) motor and an alternating current (AC) motor depending on power used. The DC motor has a commutator and a brush. Due to a mechanical contact between the commutator and the brush, reliability of the DC motor is lowered and a lifespan thereof may be shortened.
An electronic switching type brushless DC (BLDC) motor using a semiconductor device also has been used. The BLDC motors may be classified into an interior rotor type and an exterior rotor type according to an arrangement of stator and rotor.
The interior rotor type motor either uses a rotor that a rotation shaft is inserted into a center of a cylindrical permanent magnet, or uses a so-called interior permanent magnet type rotor that a rotation shaft is inserted into a center of a rotor core having electrical steel sheets stacked thereon and then a plurality of permanent magnets are inserted in the rotor core.
The interior permanent magnet type rotor has a core on which a plurality of circular electrical steel sheets are stacked for insulation. The core includes a shaft hole formed there through such that a rotation shaft can be inserted therein. Also, the core includes permanent magnet holes passed through a periphery of the shaft hole such that a plurality of permanent magnets can be positioned therein in an axial direction.
The interior permanent magnet type rotor has a flux barrier defined at both end regions of each permanent magnet for reducing a leakage of flux of each permanent magnet. However, the interior permanent magnet type BLDC motor having the interior permanent magnet type rotor may generates a relatively great torque ripple, resulting in the chance of an occurrence of relatively high vibration and noise.